Hydrocatalytic cracking of nitrogen containing wax distillates to produce middle oils



Feb. 20, 1968 K. TUPMAN ETAL 3,369,995

HYDROCATALYTIC CRACKING OF NITROGEN CONTAINING WAX DISTILLATES TO PRODUCE MIDDLE OILS Filed July 15, 1965 mvs ommuu Run 1- 1-0 vlvlhr. 4 LT]. conversion/puss Run Z- M v/vl hr. 50% conversion! pass Run3- 0- vlvlhr. 50% conversion! puss INVENTORS.

KENNETH TUPMAN DONALD RICHARD lRVlNG BY MORGAN, FINNEGAN, DURHAM 8 PINE ATTORNEYS 3,369,995 HYDROCATALYTIC CRACKING F NITROGEN CONTAINING WAX DISTILLATES T0 PRO- DUCE MIDDLE OILS Kenneth Tupman, Feltham, and Donald Richard Irving, Nunhead, London, England, assignors to The British Petroleum Company Limited, London, England, a corporation of England Filed July 13, 1965, Ser. No. 471,530 Claims priority, application Great Britain, Aug. 27, 1964, 35,131/64 1 Claim. (Cl. 208111) This invention relates to the hydrocatalytic cracking of the petroleum fractions boiling in the wax distillate range to give primarily middle distillate. Wax distillate is defined as material boiling within an ASTM boiling range of 300 to 650 C., and middle distillate as material boiling within an ASTM boiling range of 175 to 375 C.

Hydrocatalytic cracking, or hydrocracking, is known as a method of increasing the amounts of lower boiling material available from a given amount of crude oil and it is also known that it can be used to produce either gasoline or middle distillate. Much of the recent emphasis has been on increasing gasoline yields, but there are areas in which the main shortage is in the middle distillate range and in which there is already a gasoline surplus. In these situations it is important that a middle distillate producing process should have a high selectivity, producing the maximum amount of middle distillate and the .minimum amount of gasoline.

In such situations the highly active gasoline producing catalysts are of little value. Although they can be adapted for middle distillate production by choosing suitably mild process conditions they do not provide high selectivity. It is, therefore, preferred to use catalysts of moderate activity under more severe conditions. However this in its turn brings its own problems of sustaining the activity of the catalysts to a point where the life of the catalyst is acceptable and where frequent regeneration can be avoided.

Another important factor affecting catalyst activity is the nitrogen content of the feedstock. In gasoline producing hydrocracking processes it is preferred to hydrocrack a low-nitrogen content feed, a preliminary denitrogenation being given if necessary. With a middle distillate producing process, however, it has been found that a onestage process gives better selectivity for middle distillate production than a two-stage process. A one-stage process is thus preferred for maximum selectivity but again this brings the correct choice of operating conditions to give a reasonable catalyst life into prominence.

The present invention is concerned with a middle distillate producing hydrocracking process which allows for the above-mentioned factors and gives a high yield of middle distillates from high nitrogen content feedstocks in a single stage.

According to the present invention, therefore, a single stage process for the production of middle distillate from Wax distillate comprises contacting a wax distillate feedstock having a nitrogen content of at least 350 ppm. with a catalyst comprising a Group VIa and one or more iron group metal hydrogenating components supported on a base of alumina combined with either 5 or 25% wt. by weight of total catalyst of silica or boria or 2 to wt. of by weight of total catalyst of fluorine at a temperature of from 720 to 860 F., a total pressure of from 1,200 to 3,000 p.s.i.g. a total space velocity of 0.4 to 1.0 v./v./hr. and a gas rate of 4,000 to 15,000 s.c.f. of hydrogen/B, separating the product into lighter than middle distillate, middle distillate and Wax distillate and recycling the wax distillate fraction to the hydrocracking United States Patent 0 ICC zone, the conversion per pass being maintained at to 70% vol. of total feed by increasing temperature during the reaction as necessary and the amount of fresh feed in the total feed being maintained substantially equal to the conversion per pass.

The total space velocity means the space velocity of total feed to the reaction (i.e. both fresh feedstock and recycled material). The conversion per pass means the conversion to lower boiling material based on the total feed to the reaction. Since the percentage of fresh feed in the total feed is the same as the conversion per pass the total conversion will be 100%.

The terms conversion and selectivity as used in this specification are defined as follows.

The preferred Group VIa metal is molybdenum and the preferred iron group metal is cobalt. Nickel may however be present in addition to or in substitution for cobalt. As in common practice these metals will be present in the form of oxides or sulphides and the preferred contents by weight of total catalyst are:

Molybdenum5 to 40% wt. (expressed as the oxide Total iron group metals1 to 15% wt. (expressed as the divalent oxide) The preferred supports are the boria-alumina and silicaalumina supports, and the preferred boria and silica contents are 10 to 25 wt. by weight of total catalyst.

The catalysts can be prepared in any convenient known manner.

The conversion per pass is, as stated above, maintained in the range 45 to 70% by volume of total feed. Increase of the conversion per pass above this level adversely affects the selectivity and also requires more severe conditions and consequently a shorter catalyst life. On the other hand, since recycle of product in the feedstock boiling range is practised, a decrease in the conversion per pass would give too low a fresh feed space velocity for reasonable economic operation.

The conversion per pass will be affected to some extent by all of the main process variables, but pressure and gas rate are preferably fixed for any given operation. Further since the conversion is maintained constant during a run by increase in temperature, it is desirable to start the run at as low a temperature as possible and hence the space velocity chosen should be such as to give an initial operating temperature with fresh catalyst in the range 720 to 780 F. Since high selectivity is a feature of the present proces and since selectivity declines with increased temperature, the upper temperature limit is fixed at 860 F. In the case of adiabatic operations, the temperatures quoted throughout this specification refer to the average reactor temperatures.

The feedstocks used are wax distillates with a high nitrogen content. Likely nitrogen contents from readily available crude oil sources will be in the range 350 to 2,000 ppm. by weight. Feedstocks with nitrogen contents in the range 350-1000 ppm. are preferred. The

total reactor efiiuent should be washed with water to remove ammonia, particularly from the recycle gas.

By operating within the limits of the present invention, it is possible to obtain catalyst lives of at least three months and selectivities for middle distillate production of from 65% Wt. (70% volume) to 75% wt. (80% vol.).

Catalyst life refers to the on stream time before the maximum operating temperature is reached. However, it has been found that the catalyst can be regenerated by oxidative burn off, provided care is taken to limit the partial pressure of steam during regeneration, for example by using an air/ inert gas mixture as the oxidizing gas. Total catalyst life before replacement is required will thus be considerably longer.

The invention is illustrated by the following examples.

Example 1 Low silica High silica Cobalt (percent wt.) 1. 8 2.1 Molybdenum (percent wt 10. 7 12. Silcon (percent wt.) 9. 35 27. 4 Alumina (percent Wt.) Balance Balance The process conditions and results obtained are shown in Table 1 below. The temperatures used were adjusted to give the required level of conversion.

TABLE 1 Feedstock Wax Distillate Pressure, p.s.i.g ,500 Space velocity, v./v./hr 1. 0 Once through gas rate, s.c.t./b 10, 000

Catalyst High silica Low silica Conversion, percent wt 50 70 50 70 Selectivity for middle distillate production, percent wt 66 57 74 69 Example 2 This example shows the greater selectivity obtained with a one-stage process as compared to a two stage process.

The feedstock used was the same as in Example 1 and the catalyst used was the low silica catalyst of Example 1. Two runs were carried out. In the first run the untreated wax distillate was used (i.e. a One stage process). In the second run the feedstock was hydrocatalytically treated to reduce the nitrogen content to 40 p.p.m. by Weight and the sulphur to 0.015% wt. and then hydrocracked (i.e. a two-stage process).

The process conditions and results obtained are shown in Table 2 below. The temperature used was adjusted to give the required level of conversion.

Once through gas rate, so. Conversion, percent wt. Selectivity for middle percent distillate production Example 3 This example gives results obtained from extended test runs.

The catalyst used was cobalt and molybdenum oxides on silica-alumina having the following composition:

Cobalt percent weight 1.75 Molybdenum do 12.7 Silicon do 9.0 Alumina do Balance Surface area m. /g 331 Form, extr-udates.

The following process conditions were kept constant throughout all runs.

Pressure p.s.i.g 1500 Gas recycle rate s.c.f./B 10,000

Water scrubbing of the recycle gas to remove ammonia was also practised on all runs.

In the first run a conversion per pass of 40% volume and a total space velocity of 1.0 v./v./hr. (0.4 v./v./hr. fresh feed, 0.6 v./v./hr. recycle feed) were chosen. The feedstock used was a wax distillate of Iranian origin having an ASTM boiling range of 310580 C., a nitrogen content of 1350 p.p.m. by weight and a sulphur content of 1.67% wt. Under these conditions the initial operating temperature was 800 F., the catalyst ageing rate was 1.4 F./day and the maximum temperature of 860 F. was reached after 45 days. The selectivity for middle distillate production, ranged from 74.9% wt. (80.5% vol.) at a temperature of 815 F. to 70.3% (75.0% vol.) at 860 F. In spite of the relatively low conversion per pass, therefore, the catalyst life was short at the space velocity used.

In a second run therefore the total space velocity was reduced to 0.4 v./v./hr. and the conversion per pass raised to 50% vol., the feedstock and other conditions remaining the same. As a consequence the initial operating temperature was reduced to 775 F. and the catalyst ageing rate dropped to 0.7 F./day. As a consequence after days operation the temperature was only 840 F.

At this point the feedstock was changed to a wax distillate of Kuwait origin having an ASTM boiling range of 331 to 568 C., a nitrogen content of 800 p.p.m. by weight and a sulphur content of 2.61% wt. As a result the temperature to maintain the conversion at 50% per pass dropped to 835 F. and the catalyst ageing rate dropped to 0.4 F./day.

As a consequence the run showed an operating temperature of 844 F. after days. At this point the feedstock was changed back to the initial feedstock and the run was terminated at 860 F. after days.

Typical selectivities during the run were Iranian feedstock:

790 F. 74.3% wt. (80.6% vol.)

815 F. 71.9% wt. (77.3% vol.)

860 F. 66.5% wt. (71.1% vol.) Kuwait feedstock:

845 F. 67.9% wt. (73.6% vol.)

In a third run, the second run was repeated on Iranian feedstock with the conversion per pass increased to 60% volume the total space velocity of 0.4 v./v./ hr. being made up of 0.24 'of fresh feed and 0.16 of recycle feed. The initial temperature required was 760 F. and although as expected the catalyst ageing rate increased to the order of 1.0" F./day the run had a length of approximately 90 days before 860 F. was reached.

Selectivity at 790 F. was 74.1% wt. (80.7% vol.) and at 860 F., 66.3% wt. (70.6% vol.).

In the accompanying graph (FIGURE 1) the operating temperature for the three runs is plotted against time and shows quite clearly the longer operating times of runs 2 and 3.

We claim:

1. A hydr'ocatalytic process for the production of middle distillates having a minimum gasoline content in a single stage operation from a high nitrogen content wax distillate feedstock which comprises, contacting the Wax distillate feedstock having a nitrogen content from 350 to 2,000 ppm. in a hydrocracking zone with a catalyst consisting essentially of from 5 to 40% wt. of molybdenum, expressed as the oxide M00 1 to Wt. of the iron group metals, expressed as the divalent oxide and a support of alumina combined with 10 to Wt. by weight of total catalyst of an oxide selected from the group consisting of silica and boria, at an initial operating temperature of from 720 to 780 F., a total pressure of from 1,200 to 3,000 p.s.i.g., a total space velocity of 0.4 to 1.0 v./v./hr. and a gas rate of 4,000 to 15,000 s.c.f. of hydrogen/B, the temperature, pressure, space velocity and gas rate being correlated so as to initiallyobtain a conversion per pass of to vol. of total feed, gradually increasing the temperature during the reaction in the range 720 to 860 F. to maintain the conversion per pass at 45 to 70% vol. of the total feed, maintaining the amount of fresh feed in the total feed substantially equal to the conversion per pass, separating the resulting product UNITED STATES PATENTS 3,153,627 10/1964 Beuther et al. 208-58 3,166,489 1/1965 Mason et al. 208-57 3,248,318 4/ 1966 White 2081 11 ABRAHAM RIME-NS, Primary Examiner.

DELBERT E. GANTZ, Examiner. 

1. A HYDROCATALYTIC PROCESS FOR THE PRODUCTION OF MIDDLE DISTILLATES HAVING A MINIMUM GASOLINE CONTENT IN A SINGLE STAGE OPERATON FROM A HIGH NITROGEN CONTENT WAX DISTILLATE FEEDSTOCK WHICH COMPRISES, CONTACTING THE WAX DISTILLATE FEEDSTOCK HAVING A NITROGEN CONTENT FROM 350 TO 2,000 P.P.M. IN A HYDROCRACKING ZONE WITH A CATALYST CONSISTING ESSENTIALLY OF FROM 5 TO 40% WT. OF MOLYBDENUM, EXPRESSED AS THE OXIDE M0O3, 1 TO 15% WT. OF THE IRON GROUP METALS, EXPRESSED AS THE DIVALENT OXIDE AND A SUPPORT OF ALUMINA COMBINED WITH 10 TO 25% WT. BY WEIGHT OF TOTAL CATALYST OF AN OXIDE SELECTED FROM THE GROUP CONSISTING OF SILICA AND BORIA, AT AN INITIAL OPERATING TEMPERATURE OF FROM 720 TO 780*F., A TOTAL PRESSURE OF FROM 1,200 TO 3,000 P.S.I.G., A TOTAL SPACE VELOCITY OF 0.4 TO 1.0 V./V./HR. AND A GAS RATE OF 4,000 TO 15,000 S.C.F. OF HYDROGEN/B, THE TEMPERATURE, PRESSURE, SPACE VELOCITY AND GAS RATE BEING CORRELATED SO AS TO INITIALLY OBTAIN A CONVERSION PER PASS OF 45 TO 70% VOL. OF TOTAL FEED, GRADUALLY INCREASING THE TEMPERATURE DURING THE REACTION IN THE RANGE 720 TO 860*F. TO MAINTAIN THE CONVERSION PER PASS AT 45 TO 70% VOL. OF THE TOTAL FEED, MAINTAINING THE AMOUNT OF FRESH FEED IN THE TOTAL FEED SUBSTANTIALLY EQUAL TO THE CONVERSION PER PASS, SEPARATING THE RESULTING PRODUCT INTO LIGHTER THAN MIDDLE DISTILLATE FRACTION, MIDDLE DISTILLATE FRACTION AND A WAX DISTILLATE FRANCTION, AND RECYCLING THE WAX DISTILLATE FRACTION BACK TO THE HYDROCRACKING ZONE TO CONSTITUTE A PART OF THE TOTAL FEED TO THE HYDROCRACKING ZONE. 